Not actually, at least here in the U.S. (especially the South where they are a delicassie) they are simply unripened tomatoes of any variety. The recipe is simple... just egg whipped with a fork, dip the tomato slices in the egg, then dipped in flour seasoned with a goodly amount of pepper and some salt. Pop into heated oil (it should be medium hot) turn once and remove when golden brown. Serve with roast beef on a sunny summer's afternoon.
Although I live in the western U.S., I grew up visiting both sets of Grandparents in the south so came to appreciate some of the more novel dishes cherished in that part of the country. Goes well with collard greens and cornbread, by the way... Oh, yeah and a cold glass of buttermilk!